The present invention relates to wireless communications, and more particularly to the sensing of wireless transmissions from a user of a spectral resource.
The radio spectrum is a limited resource that should be shared between many different types of equipment such as cellular, home network, broadcast, and military communication equipment. Historically, each part of the radio spectrum has been allocated to a certain use (called a “licensed” and/or “primary” use). This strategy has resulted in all applications/uses being disallowed on the allocated carrier frequency except for those applications included in the license agreement. In practice, this results in large parts of the radio spectrum being unused much of the time. For instance, in the Ultra-High Frequency (UHF) band, where TV broadcasts take place, large geographical areas are unused, mainly due to the large output power needed for such applications; this large output power compels a large reuse distance in order to minimize the risk of interference. An example of such geographical areas within Scandinavia is illustrated in FIG. 1. In FIG. 1, the shaded areas represent geographic locations in which a given carrier frequency is being used by a licensed user (e.g., by Broadcast TV). In the remaining areas, the so-called “white spaces”, the given carrier frequency is allocated to the licensed user but is not actually being used by that user.
In order to make better use of the licensed spectral resources, some countries will, in the future, allow unlicensed services (so called “secondary” uses) to take place in areas (called “white spaces”) in which the licensed (primary or “incumbent”) user is not transmitting. However the primary user will always have priority for the use of the spectrum to the exclusion of others. Therefore, some sort of mechanism needs to be in place to ensure that the unlicensed users are not causing interference to the licensed user.
One mechanism is to install the unlicensed network in a geographical area where at least some parts of the licensed spectra are known to be unused.
However, even more use of the white space can be made if the non-interference mechanism adopts a detection strategy in which it operates on the licensed frequency (or frequencies) in the white space only so long as no licensed user transmissions are detected, and ceases such operation as soon as licensed user transmissions are detected. In this context, ceasing operation may mean ceasing all operation, or alternatively may mean ceasing operation only on those frequencies that are detected as being “in use”, and otherwise continuing to operate on other frequencies in the white space. Detection of power or other signal strength measurements indicative of power being present on a given frequency band is used to indicate active use on that radio spectrum. An example of a white space system currently being standardized is IEEE 802.22.
Another consideration regarding the sensing of the licensed user's transmissions is placement of the sensors. When the secondary (e.g., unlicensed) use is for cellular telecommunications, one solution is to include the sensors in the base station of the mobile communication system. Sometimes, the base station's (or network's) own sensors do not provide enough information (e.g., information about the geographical positions of active white space transmitters) for the base stations to have a clear picture of white space spectrum availability as a function of geographical position. Without this information, it is difficult for a base station to use the white space fully. To compensate for this lack of information, it may be necessary to impose quite wide safety margins (for example with respect to frequency and/or power) in order to prevent the unlicensed user's interfering with the primary (licensed) user's use of white space frequencies.
As an alternative to locating the sensors at the base station, dedicated sensors can be distributed throughout the white space. However, this increases the complexity and cost of network implementation within the white space.
An alternative way of achieving a distributed set of sensors throughout the white space is to have sensing performed by each of the mobile terminals that are located within the white space. Each of these mobile terminals performs a sensing operation, and reports its findings to a main node (e.g., the mobile terminal's serving base station), the findings being either in the form of raw data or as some sort of processed data.
A problem that is encountered with respect to the white space radio scenario is the lack of regulation when it comes to interferers. Since this information is not known by the system, information about available spectrum must be collected and analyzed by the system before initiating any data transmission. More particularly, in a white space radio scenario, a User Equipment (UE) may, acting in the capacity of white space sensor, be responsible for using its own antenna(s) to sense (measure) the received power of radio signals within different parts of the radio spectrum. For example, a UE may have the task of sensing which DVB-T channels have a received power above some certain threshold. (The pattern of where the channels may appear in the spectrum is most certainly known.) One might also consider the use of a positioning system like GPS in combination with a database (e.g., stored in the UE and optionally received from a server) to enable further details to be made available regarding expected channel use patterns with respect to a given position.
Today, this type of sensing function may be performed one channel at a time. The sensing of a single channel is permitted to continue until the probability of having a received power above the certain threshold is less than some acceptable probability threshold. However, the time spent sensing each single channel one-by-one adds up, resulting in quite some time for the whole sensing task. The sensing task may thus consume a great deal of time, processor resources and/or battery, especially if it has to be done often and for a large total spectrum.
It is therefore desirable to have ways of sensing at the UE that save time, processor resources, and/or battery resources compared to today's ways of doing it.